1. Field of the Invention
The present invention relates to a multilayered printed circuit board and a manufacturing method therefor, and more particularly to a method of manufacturing a multilayered printed circuit board with which an opening is formed by using laser beam and by forming a plated film in the opening to form a via hole, an opening in a solder-resist layer and an opening for forming a through hole. The present invention relates to the structure of a substrate which is a core.
2. Background Art
A method of manufacturing a multilayered printed circuit board has been suggested in Japanese Patent Laid-Open No. 9-130038 which uses a so-called conformal mask such that a conductive layer is formed on the surface of an insulating resin layer. Moreover, an opening is formed in a portion of the conductive layer by etching, followed by irradiating the opening with a laser beam to form an opening in the insulating resin layer.
The foregoing technique, which uses a thick copper film having a thickness of 12 mm to 18 mm as the conformal mask, encounters a large thermal conductivity, causing heat to easily be dispersed. Hence it follows that a high output laser beam or a pulse-shape laser beam must be applied a multiple of times. Therefore, when the opening is formed in the insulating resin layer, undercut occurs with which the opening is widened in the lateral. If a via hole is formed by applying an electrolytic copper plated film and an electroless copper plated film to the opening, separation of the electrolytic copper plated film and the electroless copper plated film easily occurs. As a result, reliability in the connection has been unsatisfactory.
To a worse extent, the foregoing technique cannot form a conductive circuit having fine pitch. In the manufacturing process, the electroless copper plated film (0.1 xcexcm to 5 xcexcm) and the copper foil (12 xcexcm to 18 xcexcm) under the resist must be removed after the electrolytic copper plated film has been performed. Therefore, the width of the conductive circuit cannot be reduced.
Since the thick copper foil is employed as the conformal mask, a via hole having a small diameter cannot be formed. In the manufacturing process, the electroless copper plated film (2 xcexcm) and the copper foil (12 xcexcm to 18 xcexcm) under the resist must be removed, the diameter of the via hole cannot easily be reduced.
To solve the foregoing problems, an object of the present invention is to suggest a multilayered printed circuit board which is capable of preventing occurrence of undercut if a conformal mask is employed.
A method disclosed in Japanese Patent Publication No. 4-3676 and using a xe2x80x9cconformal maskxe2x80x9d has the steps of previously forming a metal layer on an insulating resin layer; etching and removing the metal layer in the portion in which a via hole will be formed; and irradiating the opening with a laser beam so that only the insulating resin layer exposed through the opening is removed. The foregoing technique, which is capable of forming a plurality of via holes in the insulating resin layer, exhibits satisfactory productivity.
However, studies performed by the inventor of the present invention have resulted in resin which is left in the opening for forming the via hole, causing the residual resin to expand and unsatisfactorily move the via hole in the upward direction. Thus, there arises a problem in that the upper and lower layers are electrically insulated from each other.
Another problem has been detected as a result of the studies performed by the inventor of the present invention in that the resin in the periphery of the opening is raised excessively and, thus, the via hole is disconnected.
A still further object of the present invention is to obtain a multilayered printed circuit board having furthermore improved reliability in the connection in the via hole portion.
On the other hand, a multilayer forming technique which employs so-called RCC (RESIN COATED COPPER: Copper film having resin) as the built-up multilayered printed circuit board has been suggested. The foregoing technique has the steps of laminating RCC on a circuit substrate; etching the copper foil to form a through hole in a portion in which the via hole will be formed; irradiating the resin layer in the through hole portion with a laser beam to remove the resin layer opening as to form an opening; and filling the opening with plating so that the via hole is formed.
Another technique has been developed as disclosed in Japanese Patent Laid-Open No. 9-36551 with which one-side circuit substrates each having a through hole filled with a conductive substance are laminated through adhesive layers so that a multilayered structure is formed.
The foregoing multilayered printed circuit board is subjected to a process for coarsening the surface of the lower conductive circuit to maintain the adhesiveness between the surface of the lower conductive circuit and the interlayer insulating resin layer.
The coarsening method is exemplified by a method (hereinafter called a xe2x80x9cCuxe2x80x94Nixe2x80x94P plating methodxe2x80x9d) of covering and coarsening the surface of the conductive circuit with a needle shape or porous plating layer made of a Cuxe2x80x94Nixe2x80x94P alloy; a coarsening method (hereinafter called a xe2x80x9cblackening and reducing methodxe2x80x9d) with which the surface of the conductive circuit is blackened (oxidized) and reduced; a coarsening method (hereinafter called a xe2x80x9csoft etching methodxe2x80x9d) which uses mixed solution of peroxide and sulfuric acid to soft-etch the surface of the conductive circuit; and a coarsening method (hereinafter called a xe2x80x9cscratching methodxe2x80x9d) with which the surface of the conductive circuit is scratched with a sandpaper or the like.
However, if the conductive circuit is coarsened by the Cuxe2x80x94Nixe2x80x94P plating method of the blackening and reducing method, followed by forming an interlayer insulating resin layer, and followed by applying a laser beam to form an opening for forming the via hole in the interlayer insulating resin layer, the coarsened surface of the conductive circuit is undesirably removed and flattened owing to the irradiation with the laser beam. Thus, there arises a problem in that the adhesiveness with the via hole formed above the coarsened surface becomes defective.
The reason for this lies in that the coarsened surface formed by the above-mentioned process is colored and, thus, the colored surface undesirably absorbs the laser beam.
When the coarsened surface has been provided for the conductive circuit by the soft etching method or the scratching method, the coarsened surface does not absorb the laser beam. Since the coarsened surface has not sufficiently been coarsened, there arises a problem in that satisfactory adhesiveness cannot be realized between the conductive circuit and the interlayer insulating resin layer.
To solve the above-mentioned problems experienced with the conventional technique, a still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method each of which is able to realize satisfactory adhesiveness with the interlayer insulating resin layer which is formed on the conductive circuit, with which flattening of the coarsened surface of the surface of the conductive circuit can be prevented when a laser beam is applied to form the via hole in the interlayer insulating resin layer and which has a via hole (conductive circuit) having satisfactory adhesiveness.
With the conventional technique, the via hole is formed by drilling a through hole in the interlayer insulating resin layer and by disposing a metal film in the through hole. Hitherto, the through hole has been formed by employing photosensitive resin to constitute the interlayer insulating resin layer and by exposing a position corresponding to the through hole through a mask on which a black circle has been drawn to sensitize the interlayer insulating resin layer so as to dissolve the non-sensitized portion corresponding to the position of the black circle.
The foregoing photolithography method, however, encounters a limitation of the smallest diameter of the through hole, the limitation being a diameter of about 80 xcexcm. Therefore, the foregoing method cannot meet a requirement for raising the density of the multilayered printed circuit board. Therefore, the inventor of the present invention has come up with an idea that the through hole is formed by using a laser beam and performed experiments. As a result, a through hole having a diameter not larger than 80 xcexcm can be formed.
However, a fact has been detected that the reliability of the via hole is unsatisfactory when the via hole has been formed by using the through hole having a diameter not larger than 80 xcexcm. The cause of the foregoing fact has been studied, thus resulting in a problem of insufficient adhesiveness between the through hole and the electroless copper plated film. That is, the via hole is formed by depositing the electroless copper plated film. Satisfactory adhesiveness cannot be realized between the through hole formed by using a laser beam and having a small diameter and the electroless copper plated film. As a result, separation of the electroless copper plated film from the through hole causes disconnection to occur.
On the other hand, the conventional photolithography technique has been performed such that the through hole is formed by performing exposure and development. Therefore, only photosensitive materials are permitted to be used. Hence it follows that the performance required for the multilayered printed circuit board cannot sometimes be satisfied.
The conventional multilayered printed circuit board suffers from unsatisfactory reliability of solder bumps. The cause has been studied, thus resulting in the insufficient adhesiveness between the through hole and the metal film. That is, the solder bump is formed by enclosing solder in a portion on a nickel plated film deposited on the surface of the conductive circuit below the opening. The adhesiveness between the conductive circuit and the nickel plated film has been unsatisfactory, causing the nickel plated film to be separated. It leads to a fact that disconnection of the solder bump occurs.
To solve the above-mentioned problems, a still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method therefor each of which is capable of forming a via hole exhibiting satisfactory reliability and having a small diameter.
To solve the above-mentioned problems, a still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method therefor each of which permits selection of high-performance material for the solder resist.
A still further object of the present invention is to provide a multilayered printed circuit board and a manufacturing method therefor each of which is capable of forming a reliable solder bump.
On the other hand, the through hole provided for a core substrate must precisely be formed. Thus, a through hole having a diameter smaller than 100 xcexcm cannot easily be formed by drilling. Therefore, the through hole is formed in a copper-plated laminated board by using a laser beam.
An optimum laser beam is a carbon dioxide laser because of a low cost from the viewpoint of industrial production. However, the carbon dioxide laser is undesirably reflected by the surface of the copper foil. Therefore, it is technical common sense that the through hole cannot be formed directly in the copper-plated laminated board by the laser machining. Thus, a technique has been disclosed in Japanese Patent Laid-Open No. S61-99596 with which the surface of the copper foil of the copper-plated laminated board is subjected to a blackening process (an oxidizing process), followed by applying a laser beam.
The foregoing technique, however, requires the blackening process to be performed first, causing a problem to arise in that a long manufacturing process is required.
As a result of energetic studies performed by the inventors of the present invention, an unexpected fact has been found that reduction in the thickness of the copper foil enables an opening to be formed in the copper foil in spite of the reflection by the surface.
To solve the above-mentioned problems, a still further object of the present invention is to realize a technique which is capable of directly forming an opening in a copper-plated laminated board and provide a substrate having the through hole formed by the foregoing method and a multilayered printed circuit board.
Since a high density and multilayered structure has been required in recent years, a built-up multilayered printed circuit board has attracted attention. The multilayered circuit board is a multilayered circuit board having a core substrate on which conductive circuits and interlayer insulating resin layers are alternately formed. The conductive circuits in the layers are connected to one another through a via hole.
As the core substrate of the foregoing built-up multilayered printed circuit board, a glass epoxy resin substrate of FR-4 grade has been employed.
However, the glass epoxy resin substrate of the FR-4 grade encounters a problem in that the insulation resistance between the through holes is reduced in a HAST test and a steam test. Another problem arises in that the resistance of the through hole chain was excessively changed as a result of the heat cycle test. That is, the reliability realized after use for a long time has been unsatisfactory.
To solve the above-mentioned problem, a core substrate which employs BT (Bis maleimide-Triazine) resin has been suggested. The foregoing substrate is, however, a costly substrate.
Inventors of the present invention have considered probability of preventing reduction in the insulation resistance between the through holes and change in the resistance of the conductive circuit for connecting the through holes to each other by using low-cost resin such as epoxy resin in place of the costly resin, such as the BT resin. As a result, an unexpected fact was found that the foregoing problem is caused from the Tg point of the resin.
According to the present invention, a low-cost multilayered printed circuit board is suggested which is free from reduction in the insulation resistance between through holes as a result of the HAST test and the steam test and change in the resistance of the conductive circuit for connecting the through holes to each other as a result of a heat cycle test.
The method of manufacturing the printed circuit board is broadly divided into a subtractive method (a Subtractive Process) and an additive method (an Additive Process). The subtractive method is also called an etching method which is characterized by chemically corroding the surface copper foil of a copper-plated laminated board. A method of manufacturing a printed circuit board (a double-side board) by the subtractive process will now briefly be described.
Initially, a copper-plated laminated board is prepared which incorporates an insulating substrate having two sides each of which is coated with copper foil having tens of xcexcm. Then, an opening for forming a through hole is formed at a predetermined position of the copper-plated laminated board by drilling or the like. If a drilling step is performed, smears occurs in the opening for forming the through hole, desmear solution is used to process the copper-plated laminated board to dissolve and remove the smears. After the desmear process has been completed, electroless copper plating of the overall ground layer constituted by copper foil and the inner surface of an opening for forming the through hole is performed so that a thin plated layer is formed. After the foregoing plating process has been completed, a mask is formed on the thin plated layer. Then, thick plated layers are formed in the portions exposed through openings of the mask by electrolytic copper plating. After the foregoing plating process has been completed, the mask is separated. Then, etching is performed in a state in which an etching resist has been formed on the thick plated layer by solder plating or the like. The etching process is so performed as to remove the thin plated layer and the ground layer so as to divide the conductive pattern. Finally, the etching resist is separated so that a required printed circuit board is manufactured.
The foregoing method, however, is impossible to accurately form a fine pattern having a satisfactory shape. The characteristics of the etching causes a so-called divergent conductive pattern having a bottom which is longer than the top to easily be formed. Therefore, a pattern cannot easily be formed in a portion (for example, a bonding pad portion) which must have a fine and precise structure.
In view of the foregoing, a still further object of the present invention is to provide a method of manufacturing a printed circuit board with which a fine conductive pattern having a satisfactory shape can be formed.
A method of manufacturing a multilayered printed circuit board according to claim 1 comprising the steps (1) to (5):
(1) pressing resin to form an interlayer insulating resin layer having a metal film formed thereon against a substrate for forming a conductor circuit;
(2) reducing the thickness of a whole surface of the metal film by etching;
(3)forming an opening in the metal film so as to expose the interlayer insulating resin layer;
(4) applying a laser beam from the formed opening of the metal film side to remove the resin forming the interlayer insulating resin layer exposed through the opening so as to provide an opening for a via hole; and
(5) depositing a plating conductor in the formed opening to form the via hole.
The present invention according to claim 1 employs a metal film thinned by etching and thus having a lowered thermal conductivity as a conformal mask. Therefore, an opening can be formed by a small output laser. Hence it follows that generation of undercut of resin for forming an interlayer insulating resin layer can be prevented.
A method of manufacturing a multilayered printed circuit board according to claim 2 comprising the steps (1) to (8):
(1) pressing resin to form an interlayer insulating resin layer having a metal film formed thereon against a substrate forming a conductor circuit;
(2)reducing the thickness of a whole surface of the metal film by etching;
(3) forming an opening in the metal film so as to expose the interlayer insulating resin layer;
(4) applying a laser beam from the formed opening of the metal film side to remove the resin forming the interlayer insulating resin layer exposed through the opening to provide an opening for a via hole;
(5) forming an electroless plated film on the substrate forming the conductor circuit;
(6) forming a plating resist on the substrate forming the conductor circuit;
(7) electrolytic-plating a portion in which the plating resist is not formed; and
(8) removing the plating resist to remove the metal film and the electroless plated film below the plating resist by etching so as to form the via hole and the conductor circuit.
The present invention according to claim 2 employs a metal film thinned by etching and thus having a lowered thermal conductivity as a conformal mask. Therefore, an opening can be formed by a small output laser. Hence it follows that generation of undercut of resin for forming an interlayer insulating resin layer can be prevented.
After an opening for forming a via hole has been formed, an electroless copper plated film is formed on the metal film. Then, an electrolytic copper plated film is formed on the electroless copper plated film. When the conductive circuit and the via hole are formed, the electroless copper plated film lower than the resist layer is removed by etching. Since the metal film and the electroless copper plated film, which are thin films, can easily be removed, the electrolytic copper plated film constituting the conductive circuit and the via hole is not corroded during the etching process. As a result, a circuit having a fine pitch and a via hole having a precise diameter can be formed.
The present invention in claim 3 according to claim 1 or 2, the metal film is copper foil.
The present invention in claim 4 according to claim 1 or 2, the thickness of the metal film is made to be 5 xcexcm to 0.5 xcexcm in the step for reducing the thickness of the metal film by performing etching.
In accordance with claim 4, the thickness of the metal film is made to be 5 xcexcm to 0.5 xcexcm. The reason for this lies in that undercut occurs if the thickness of the metal film is larger than 5 xcexcm. If the thickness is not larger than 0.5 xcexcm, the function of the conformal mask cannot be obtained.
In accordance with claim 5, an interlayer insulating resin layer incorporating a metal film having a thickness of 5 xcexcm to 0.5 xcexcm is pressed against a substrate having a conductive circuit formed thereon.
In the present invention, the resin film having a metal film formed previously is pressed. Therefore, satisfactory flexibility can be realized which permits the resin film to easily be pressed against the substrate having the conductive circuit formed thereon.
According to the present invention, a method of manufacturing a multilayered printed circuit board is provided, incorporating a substrate on which a lower conductive circuit is formed, an insulating resin layer and an upper conductive circuit formed on the lower conductive circuit and having a structure that the lower conductive circuit and the upper conductive circuit are connected to each other through a via hole, the method of manufacturing a multilayered printed circuit board comprising the steps of: forming the lower conductive circuit on the substrate; forming the insulating resin layer on the lower conductive circuit; forming a coarsened surface on the surface of the insulating resin layer; forming, on the coarsened surface, a metal layer having an opening through which a portion of the coarsened surface is exposed; irradiating the coarsened surface exposed through the opening with a laser beam to remove the insulating resin layer to form an opening for the via hole; and forming the upper conductive circuit and the via hole.
According to the present invention, a method of manufacturing a multilayered printed circuit board is provided, incorporating a substrate on which a lower conductive circuit is formed, an insulating resin layer and an upper conductive circuit formed on the lower conductive circuit and having a structure that the lower conductive circuit and the upper conductive circuit are connected to each other through a via hole, the method of manufacturing a multilayered printed circuit board comprising the steps of: forming the lower conductive circuit on the substrate; laminating, heating and compressing metal foil having a coarsened surface formed either surface thereof and the insulating resin layer formed on the coarsened surface such that the insulating resin layer makes contact with the lower conductive circuit so that the metal foil is integrated; etching a portion of the metal foil to form an opening to expose the coarsened surface of the insulating resin layer; irradiating the coarsened surface exposed through the opening with a laser beam to remove the insulating resin layer so as to form an opening for forming the via hole; and forming the upper conductive circuit and the via hole.
As a result of energetic studies performed by the inventors of the present invention, a fact has been found that the cause of residues produced in the operation for forming the opening for forming the via hole is the structure that the surface which is irradiated with the laser beam is a mirror surface which reflects the laser beam to inhibit complete removal of the insulating resin layer.
The present invention uses the detected fact such that the surface irradiated with the laser beam is formed into the coarsened surface to prevent reflection of the laser beam.
In the present invention, the resist against the laser beam is metal layer or metal foil. Moreover, the opening is formed in the metal layer or the metal foil. The opening is irradiated with a laser beam capable of realizing a diameter of a spot light which is larger than the diameter of the opening so that the opening for forming the via hole is formed in the insulating resin layer.
In the present invention, the surface of the insulating resin layer exposed through the opening in the metal layer or the like is formed into the coarsened surface. Therefore, reflection of the laser beam can be prevented and the insulating resin layer can completely be removed. Since upward expansion of the periphery of the insulating resin layer can be prevented, also disconnection of the via hole can be prevented.
Although the reason why the expansion can be prevented cannot clearly be detected, an estimation can be made that the coarsened surface has a high absorption with respect to a laser beam and the resin is easily formed into plasma.
The inventors of the present invention have energetically studied in order to realize the foregoing object. As a result, etching solution containing a cupric complex and organic acid is used to etch the conductive circuit. Thus, flattening can be prevented when the surface of the conductive circuit is irradiated with a laser beam. Moreover, a coarsened surface exhibiting satisfactory adhesiveness with the interlayer insulating resin layer formed on the conductive circuit and the via hole can be formed. The foregoing detected fact is used to establish the present invention having the following essential portion.
A multilayered printed circuit board according to claim 12 comprising: a substrate on which a conductive circuit is formed; an interlayer insulating resin layer formed on the conductive circuit; an opening for forming a via hole formed in the interlayer insulating resin layer; and another conductive circuit including a via hole and formed on the interlayer insulating resin layer, wherein
the surface of the conductive circuit is subjected to a coarsening process using etching solution containing cupric complex and organic acid, and
stripe pits and projections are formed on the inner wall of the opening for forming the via hole.
According to claim 13, a method of manufacturing a multilayered printed circuit board including (1) a step of forming a conductive circuit; (2) a step of forming an interlayer insulating resin layer on the conductive circuit; (3) a step of applying a laser beam to form an opening for forming a via hole in the interlayer insulating resin layer; and (4) a step of forming another conductive circuit including a via hole on the interlayer insulating resin layer, wherein
the surface of the conductive circuit is subjected to a coarsening process by using etching solution containing cupric complex and organic acid.
It is preferable that the method of manufacturing the multilayered printed circuit board has the step of spraying etching solution containing the cupric complex and the organic acid to the surface of the conductive circuit or the conductive circuit is immersed in the etching solution under a bubbling condition so that the surface of the conductive circuit is subjected to the coarsening process.
In claim 15, a multilayered printed circuit board incorporating interlayer insulating resin layers and conductive layers laminated alternately and structured such that the conductive layers are connected to one another through via holes each of which is formed by forming a metal film in a through hole formed in each of the interlayer insulating resin layers, said multilayered printed circuit board according to the present invention comprising:
stripe pits and projections formed on the side wall of the through hole.
An aspect of the present invention according to claim 15 has the structure that stripe pits and projections are provided for the side wall of the through hole. Thus, the area of connection with the metal film can be enlarged, causing the adhesiveness to be improved. Thus, a reliable via hole can be formed.
Since the stripe pits and projections are formed in the direction of the opening, separation of the via hole can be prevented if force is exerted in the vertical direction of the via hole. Therefore, if the resin is left in the through hole for forming the via hole and the residue is expanded owing to heat to upwards move the via hole, separation can be prevented and reliability can be maintained in the connection.
The bump is provided for the via hole. If an element, such as an IC chip, having a different coefficiency of thermal expansion is mounted, force is exerted in the vertical direction of the via hole owing to the heat cycle. Also in the foregoing case, the stripe pits and projections in the direction of the opening prevent separation of the via hole.
It is preferable that the stripe pits and projections have the structure that the intervals between projections (or pits) are 1 xcexcm to 20 xcexcm. If the interval is too long or too short, the adhesiveness effect with the metal film deteriorates. The foregoing interval is substantially the same as xc2xd of the wavelength of the laser beam.
It is preferable that the metal film for forming the via hole is formed such that the electroless copper plated film and the electrolytic copper plated film are formed in this order from a position adjacent to the side wall of the through hole. The electroless copper plated film is harder than the electrolytic copper plated film. Moreover, the stripe pits and projections are formed into a pseudo coarsened surface. Therefore, if separating force is exerted, breakage of the metal film does not cause the via hole to be separated from the through hole.
It is most preferable that a coarsened surface having an average surface roughness Ra of about 0.05 xcexcm to about 5 xcexcm is formed (FIG. 31(A) which is an enlarged view) on the surface of the stripe pits and projections. The reason for this lies in that the adhesiveness can furthermore be improved.
When the coarsened surface of the sidewall of the through hole is complicated, transmission of a high-frequency signal causes delay in transmission to occur and noise to be produced owing to the skin effect. The stripe pits and projections according to the present invention are formed at the intervals of 1 xcexcm to 20 xcexcm. Therefore, the skin effect does not raise a critical problem. Moreover, the adhesiveness can be improved.
It is most preferable that the surface of the conductive circuit to which the through hole reaches is made of an electrolytic copper plated film. The electrolytic copper plated film has small crystal particles as compared with those of the electroless copper plated film. Moreover, the electrolytic copper plated film exhibits excellent glossiness to easily reflect a laser beam. Therefore, the electrolytic copper plated film is an optimum film in a case where incident light of the laser beam and reflected light are caused to interfere with each other as described later.
It is preferable that the surface of the conductive circuit to which the through hole reaches has a metal coarsened layer.
When the metal coarsened layer is formed on the surface of the conductive circuit, the laser beam is reflected by the surface of the metal coarsened layer to enable the laser beam to be reflected by the surface of the metal coarsened layer to cause the incident light of the laser beam and the reflected wave to interfere with each other. Thus, the stripe pits and projections formed in the direction of the opening can be provided for the surface of the wall of the through hole of the interlayer insulating resin layer.
Since the coarsened layer enables the reflection of the laser beam to be prevented to a level not higher than a predetermined level, residual resin on the surface of the conductive circuit can be prevented. Since the coarsened layer enables the adhesiveness with the interlayer insulating resin layer to be maintained, separation of the interlayer insulating resin layer owing to deterioration in the thermal shock of the laser beam can be prevented.
When the coarsened layer is not provided, the reflection is raised excessively, causing residue of the resin to easily occur. If an oxidizing (a blackening) process is performed to form the coarsened layer, the laser beam is undesirably absorbed. Thus, the laser beam cannot be reflected.
It is preferable that Rj of the coarsened layer is 0.05 xcexcm to 20 xcexcm. If Rj is 0.05 xcexcm or smaller, the reverse side is blackened. Thus, the laser beam is undesirably absorbed. If Rj is larger than 20 xcexcm, the laser beam scatters. In either of the two cases, incident light a reflected wave cannot cause to interfere with each other.
It is preferable that the coarsened layer is a coarsened layer obtained by non-acidic chemical coarsening process, such as physical coarsening including a polishing process, an oxidizing (a blackening) and reducing process, a process using sulfuric acid and hydrogen peroxide solution or a coarsening process using etching solution composed of cupric complex and organic acid under coexistence of oxygen. As an alternative to this, it is preferable that the coarsened layer is a coarsened layer obtainable from a plating process using an alloy, such as Cuxe2x80x94Nixe2x80x94P or Cuxe2x80x94Coxe2x80x94P. The reason for this lies in that the foregoing coarsened layer is able to reflect the laser beam.
Plating of Cuxe2x80x94Nixe2x80x94P may be performed by using electroless plating bath, the pH of which is 9 and which is water solution of, for example, copper sulfate (0.1xc3x9710xe2x88x922 to 25xc3x9710xe2x88x922 mol/l), nickel sulfate (0.1xc3x9710xe2x88x923 to 40xc3x9710xe2x88x923 mol/l), citric acid (1xc3x9710xe2x88x922 to 20xc3x9710xe2x88x922 mol/l), sodium hypophosphite (1xc3x9710xe2x88x921 to 10xc3x9710xe2x88x921 mol/l), boric acid (1xc3x9710xe2x88x921 to 10.0xc3x9710xe2x88x921 mol/l) or a surface active agent (Surfinol 465 manufactured by Nissin Chemical Industry) (0.1 g/l to 10 g/l).
It is preferable that the cupric complex according to the present invention is a cupric complex of azole. The cupric complex of azole is employed as an oxidizer for oxidizing metal copper. The azole may be diazole, triazole or tetra azole. Among the foregoing materials, it is preferable that any one of the following material is employed: imidazole, 2-methyl imidazole, 2-ethyl imidazole, 2 ethyl-4-methyl imidazole, 2-phenyl imidazole or 2-undecyl imidazole. It is preferable that the quantity of cupric complex of azole which must be added is 1 wt % to 15 wt %. The reason for this lies in that noble metal, such as Pd, exhibiting satisfactory solubility, stability and constituting crystal core can be dissolved.
To dissolve copper oxide, organic acid is mixed with the cupric complex of azole.
Specifically, it is preferable that the organic acid is at least one type of material selected from a group consisting of formic acid, acetic acid, propionic acid, butyric acid, valerianic acid, capronic acid, acrylic acid, crotonic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, maleic acid, benzoic acid, glycollic acid, lactic acid, malic acid and sulfamic acid. It is preferable that the content of the organic acid is 0.1 wt % to 30 wt % to maintain the solubility of oxidized copper and dissolution stability.
The produced cuprous complex is dissolved owing to an action of the acid so as to be combined with oxygen so that cupric complex is produced which is again contributed to the oxidation of copper.
To assist the dissolution of copper and oxidation of azole, halogen ions, for example, fluorine ions, chlorine ions or bromine ions, may be added to the etching solution. In the present invention, hydrochloric acid or sodium chloride may be added to supply halogen ions. It is preferable that the quantity of halogen ions is 0.01 wt % to 20 wt % to improve the adhesiveness between the formed coarsened surface and the interlayer insulating resin layer.
The cupric complex of azole and the organic acid (and halogen ions if necessary) are dissolved in water to adjust the etching solution.
The oxidizing and reducing process may be performed by using an oxidizing bath of 1 g/l to 100 g/l NaOH, 1 g/l to 100 g/l NaClO2 and 1 g/l to 50 g/l Na3PO4 and a reducing bath of 1 g/l to 100 g/l NaOH to 1 g/l to 50 g/l NaBH4.
The metal coarsened layer may be coated with at least one type of metal materials selected from a group consisting of Ti, Al, Cr, Zn, Fe, In, Tl, Co, Ni, Sn, Pb, Bi and noble metal to maintain glossiness and improve adhesiveness with the solder resist. It is preferable that the thickness of the selected metal material is 0.01 xcexcm to 10 xcexcm.
In the present invention, it is preferable that the diameter of the through hole for forming the via hole is 80 xcexcm or smaller. The foregoing precise via hole has a small area of contact between the metal film for forming the via hole and the side wall of the through hole for forming the via hole. Therefore, separation considerably easily occurs. Therefore, the formation of the conventional coarsened surface cannot satisfactorily prevent the separation. If the coarsened surface is made to be excessively complicated, the foregoing skin effect problem of delay in transmission and production of noise arises. The present invention is able to overcome the foregoing problems.
The present invention in claim 16 according to claim 15, the interlayer insulating resin layer is made of thermosetting resin or a composite material of the thermosetting resin and thermoplastic resin.
An aspect of the present invention according to claim 16 has a structure that the interlayer insulating resin layer is made of thermosetting resin or a composite material of thermosetting resin and thermoplastic resin. Therefore, stripe pits and projections can easily be formed owing to interference of the laser beam. Note that only the thermosetting resin, which encounters dissolution of resin, cannot form clear stripe pits and projections.
The present invention in claim 17 according to claim 15, the interlayer insulating resin layer contains acrylic monomer.
It is preferable that an aspect of the present invention according to claim 17 is structured such that the interlayer insulating resin layer contains acrylic monomer. The reason for this lies in that residues of the resin can be reduced.
The acrylic monomer crosslinks monomer or oligomer of the thermosetting resin (including the thermosetting resin, a portion of which has been sensitized).
The acrylic monomer can be decomposed relatively easily. Therefore, the acrylic monomer is contained in the molecular chain, the acrylic monomer is decomposed owing to a laser beam, causing the thermosetting resin to have low molecular weight. Moreover, the resin having the low molecular weight is decomposed by the laser beam. Therefore, formation into plasma can easily be formed, causing residue of resin to substantially be eliminated.
The acrylic monomer may be any one of a variety of commercial products. For example, DPE-6A KAYAMAER PM-2 or PM-21 manufactured by Nihon Kayaku, R-604 manufactured by Kyoei or Aronix M-315, M-325 or M-215 manufactured by Toa may be employed.
DPE-6A is expressed by chemical formula 1 shown in FIG. 59, R-604 is expressed by chemical formula 2, Aronix M-315 is expressed by chemical formula 3, M215 is expressed by chemical formula 4 shown in FIG. 60 and KAYAMAER PM-2 and PM-21 is expressed by chemical formula 5.
A method of manufacturing a multilayered printed circuit board according to claim 18 comprising at least the steps (a) to (d):
(a) forming a conductive circuit;
(b) coating the conductive circuit with resin;
(c) irradiating the resin with a carbon-dioxide gas laser beam to form a through hole which reaches the conductive circuit such that the carbon-dioxide gas laser beam is vertically applied to the conductive circuit below the resin to cause interference of reflected wave from the conductive circuit and incident wave to occur so that stripe pits and projections are formed on the side wall of the through hole; and
(d) coating the through hole with metal to form a via hole.
In claim 18, an aspect has a structure that the conductive circuit below the resin is vertically irradiated with a carbon-dioxide-gas laser beam to cause interference between reflected wave from the conductive circuit and incident wave to occur. Therefore, the stripe pits and projections can be formed on the side wall of the through hole. Therefore, the adhesiveness with metal can be improved so that a reliable via hole can be formed.
The present invention in claim 19 according to claim 18, the resin is thermosetting resin or a composite material of the thermosetting resin and thermoplastic resin.
An aspect of claim 19 has a structure that the interlayer insulating resin layer is made of the thermosetting resin or a composite of the thermosetting resin and thermoplastic resin. Therefore, the stripe pits and projections can easily be formed by the laser beam.
The present invention in claim 20 according to claim 18, the step of forming the via hole includes a step of forming a resist after an electroless copper plated film has been formed in the through hole and supplying electric power through the electroless plated film to form an electrolytic plated film in a portion in which the resist is not formed.
An aspect of claim 20 has a structure that an electroless copper plated film is formed on the surface of the through hole, followed by forming a resist. Then, electric power is supplied through the electroless copper plated film to form an electrolytic copper plated film in a portion in which no resist is formed. Thus, the via hole is formed. Since the stripe pits and projections are formed on the side wall of the through hole by using the interference of the laser beam and then the electroless plated film is formed, the adhesiveness between the electroless copper plated film and the through hole in the interlayer insulating resin layer can be improved. As a result, a reliable via hole can be formed.
The present invention in claim 21 according to claim 18, the interlayer insulating resin layer contains acrylic monomer.
A method of manufacturing a printed circuit board according to claim 22 comprising at least the steps (a) and (b):
(a) forming a solder-resist layer on the surface of a substrate on which a conductive circuit has been formed; and
(b) irradiating the solder-resist layer with a laser beam to form a through hole which reaches the conductive circuit.
An aspect claim 22 has a structure that the through hole is formed in the solder resist layer by using the laser beam. Therefore, the material is not limited to the photosensitive material. As a material of the solder-resist layer, any one a variety of materials may be employed.
Moreover, defective conduction owing to residue of the solder-resist resin can be prevented.
It is most preferable that the surface of the conductive circuit is constituted by the electrolytic plated film. The electrolytic plated film has large crystal particles as compared with those of the electroless plated film. Moreover, the electrolytic plated film exhibits excellent glossiness to easily reflect a laser beam. Therefore, the electrolytic plated film is an optimum film in a case where incident light of the laser beam and reflected light are caused to interfere with each other as described later.
The present invention in claim 23 according to claim 22, the surface of the conductive circuit has a metal coarsened layer.
An aspect of claim 23 is characterized in that the surface of the conductive circuit has a metal coarsened layer.
Since the metal coarsened layer is formed on the surface of the conductive circuit, the laser beam can be reflected by the surface of the metal coarsened layer. Thus, as described later, incident waves of the laser beam and reflected waves can be caused to interfere with each other. Thus, the stripe pits and projections formed in the direction of the opening can be provided for the wall of the through hole of the solder-resist layer.
The present invention in claim 24 according to claim 22, (c) a step of forming a bump made metal having a low melting point in the through hole is performed after the step (b).
An aspect claim 24 has a structure that a bump made of a low-melting-point metal is provided for the through hole in the solder-resist layer. Thus, an electrode of an IC chip can be connected to the foregoing bump or the foregoing bump may be used to mount the printed circuit board to another printed circuit board.
The present invention in claim 25 according to claim 22, a laser beam in a single mode is applied in the step of forming the through hole so that a through hole having a diameter of 300 xcexcm to 650 xcexcm is formed.
An aspect of claim 25 has a structure that a single-mode laser beam, the diameter of a spot light of which can be enlarged is applied. Therefore, a through hole for forming a through hole having a diameter of 300 xcexcm to 650 xcexcm, that is, a through hole for forming a bump for establishing the connection with another printed circuit board (for example, a mother board) can be formed in the solder-resist layer.
The present invention in claim 26 according to claim 22, a laser beam in a multi mode is applied in the step of forming the through hole so that a through hole having a diameter of 50 xcexcm to 300 xcexcm is formed.
An aspect of claim 26 has a structure that a multimode laser beam, the diameter of which can be reduced is applied. Therefore, a through hole for forming a through hole having a diameter of 50 xcexcm to 300 xcexcm, that is, a through hole for forming a bump for establishing the connection with an IC chip can be formed in the solder-resist layer.
The present invention in claim 27 according to any of claims 22 to 26, the step of forming the through hole is performed such that the carbon-dioxide gas laser beam is vertically applied to the conductive circuit below the resin to cause interference of reflected wave from the conductive circuit and incident wave to occur so that stripe pits and projections are formed on the side wall of the through hole.
An aspect claim 27 has a structure that a step for forming the through hole is arranged such that reflected wave of the carbon-dioxide gas laser beam and the incident wave are caused to interfere with each other. Thus, the stripe pits and projections are formed on the side wall of the through hole. Therefore, when the metal film is provided for the through hole, the metal film can be brought into hermetic contact with the through hole.
The present invention in claim 28 according to claim 27, the step of forming the bump is performed such that a metal film is provided for the through hole having the side wall provided with the stripe pits and projections, and then metal having a low melting point is enclosed.
An aspect of claim 28 has a structure that the metal film is provided for the through hole having the side wall. Then, low-melting-point metal is enclosed to form the bump. The metal film is brought into hermetic contact with the through hole having the stripe pits and projections so that the bump is strongly connected to the conductive circuit.
In claim 29, a printed circuit board incorporating a substrate provided with a conductive circuit and having a surface on which a solder-resist layer is formed, said printed circuit board according to the present invention comprising:
stripe pits and projections formed on the side wall of a through hole formed in the solder-resist layer.
An aspect of claim 29 has a structure that the stripe pits and projections are formed on the side wall of the through hole formed in the solder-resist layer. Therefore, when the metal film is formed on the surface of the through hole, the metal film can strongly be brought into hermetic contact with the through hole.
A heat cycle sometimes causes a crack to sometimes occur in the solder-resist layer owing to the difference between the coefficiency of thermal expansion of the metal film and that of the solder-resist layer. However, the present invention causes the metal film and the wall of the through hole of the solder-resist layer to be brought into hermetic contact to each other. Therefore, a crack cannot easily be formed.
Since the stripe pits and projections are provided for the wall of the through hole in the direction of the opening, the contact between the wall and the low-melting-point metal is made to be line contact in place of the plane contact. Therefore, a phenomenon (migration) that the low-melting-point metal is ionized and diffused under hot and high humidity conditions can be prevented. The employed low-melting-point metal and the metal film are the same as those described above. It is most preferable that the surface of the conductive circuit is constituted by an electolytically plated film. The electolytically plated film has smaller crystal particles as compared with the electroless platted film and exhibiting excellent glossiness. Moreover, discoloration, called xe2x80x9ccolor change owing to platingxe2x80x9d can be prevented. Thus, the laser beam can easily be reflected. Thus, the stripe pits and projections can be formed on the surface of the wall in the direction of the opening.
It is preferable that the stripe pits and projections have the structure that the intervals between projections (or pits) are 1 xcexcm to 20 xcexcm. If the interval is too long or too short, the adhesiveness effect with the metal film deteriorates. A similar state is realized to that realized by the plane contact and, therefore, the foregoing effect cannot be obtained. The foregoing interval is substantially the same as xc2xd of the wavelength of the laser beam.
The low-melting-point metal may be solder, such as Sn/Pb, Ag/Sn or Ag/Sn/Cu. The foregoing bump can be formed through a metal film made of Ni/Au, Ni/Pd/Au, Cu/Ni/Au or Cu/Ni/Pd/Au. Adjustments are performed such that the thickness of the Cu layer and that of the Ni layer is 0.1 xcexcm to 10 xcexcm and that of each of the Pd layer and the Au layer is 0.01 xcexcm to 10 xcexcm.
The present invention in claim 30 according to claim 29, a bump made of metal having a low melting point is formed in the through hole through a metal film.
An aspect of claim 30 has a structure that the low-melting-point metal is enclosed to form the bump. When the metal film is brought into hermetic contact with the through hole having the stripe pits and projections, the bump can strongly be connected to the conductive circuit.
The present invention in claim 31 according to claim 29 or 30, the solder-resist layer is made of thermosetting resin or a composite material of the thermosetting resin and thermoplastic resin.
An aspect of claim 31 has a structure that the solder-resist layer is constituted by thermosetting resin or a composite of the thermosetting resin and the thermoplastic resin. Therefore, the stripe pits and projections can easily be formed on the side surface of the through hole by the laser beam. When only the thermoplastic resin is employed, the resin is undesirably dissolved. Thus, clear pits and projections cannot be formed.
The present invention in claim 32 according to any of claims 29 to 31, a coarsened layer is formed on the surface of the conductive circuit.
An aspect of claim 32 is characterized in that the surface of the conductive circuit has a metal coarsened layer.
Since the metal coarsened layer is formed on the surface of the conductive circuit, the laser beam can be reflected by the surface of the metal coarsened layer. Thus, the incident wave and the reflected wave of the laser beam can be caused to interfere with each other. Thus, the stripe pits and projections can be formed on the surface of the wall of the through hole in the solder-resist layer in the direction of the opening.
In the present invention, it is desirable to use an adhesive for electroless plating as the above interlayer resin insulating layer. In this adhesive for electroless plating, it is optimal that heat resisting resin particles soluble to a hardened acid or oxidizing agent are dispersed into unhardened heat resisting resin difficult to be soluble to an acid or an oxidizing agent.
The heat resisting resin particles are dissolved and removed by processing these resin particles using an acid or an oxidizing agent and a coarsened face constructed by an anchor formed in the shape of an octopus trap can be formed on a layer surface.
In the above adhesive for electroless plating, the above heat resisting resin particles particularly hardened are desirably constructed by using {circle around (1)} heat resisting resin powder having an average particle diameter equal to or smaller than 10 xcexcm, {circle around (2)} cohesive particles formed by aggregating heat resisting resin powder having an average particle diameter equal to or smaller than 2 xcexcm, {circle around (3)} a mixture of heat resisting powder resin powder having an average particle diameter from 2 to 10 xcexcm and heat resisting resin powder having an average particle diameter equal to or smaller than 2 xcexcm, {circle around (4)} pseudo-particles in which at least one kind of heat resisting resin powder or inorganic powder having an average particle diameter equal to or smaller than 2 xcexcm is attached to the surface of heat resisting resin powder having an average particle diameter from 2 to 10 xcexcm, {circle around (5)} a mixture of heat resisting powder resin powder having an average particle diameter from 0.1 to 0.8 xcexcm and heat resisting resin powder having an average particle diameter greater than 0.8 xcexcm and smaller than 2 xcexcm, and {circle around (6)} heat resisting powder resin powder having an average particle diameter from 0.1 to 1.0 xcexcm. This is because these materials can form a more complicated anchor.
A depth of the coarsened face is preferably set to secure a close attaching property such that Rj=0.01 to 20 xcexcm. In particular, Rj preferably ranges from 0.1 to 5 xcexcm in the semi-additive method since an electroless plating film can be removed while the close attaching property is secured.
The heat resisting resin difficult to be soluble to an acid or an oxidizing agent mentioned above is desirably constructed by xe2x80x9ca resin complex constructed by thermosetting resin and thermoplastic resinxe2x80x9d, or xe2x80x9ca resin complex constructed by photosensitive resin and thermoplastic resinxe2x80x9d. The former has a high heat resisting property. The latter is desirable since the opening for the via hole can be formed by photolithography.
The above thermosetting resin can be constructed by using epoxy resin, phenol resin, polyimide resin, etc. When the thermosetting resin is photosensitized, a thermosetting group acrylic-reacts on methacrylic acid, acrylic acid, etc. Acrylate of the epoxy resin is particularly optimal.
The epoxy resin can be constructed by using epoxy resin of novolak type such as phenol novolak type, cresol novolak type, etc., dicyclopentadiene-modified alicyclic epoxy resin, etc.
The thermoplastic resin can be constructed by using polyether sulfone (PES), polysulfone (PSF), polyphenylene sulfone (PPS), polyphenylene sulfide (PPES), polyphenyl ether (PPE), polyether imide (PI), etc.
A mixing ratio of the thermosetting resin (photosensitive resin) and the thermoplastic resin is preferably set such that thermosetting resin (photosensitive resin)/thermoplastic resin=95/5 to 50/50. This is because a high toughness value can be secured without reducing a heating resisting property.
A mixing weight ratio of the above heat resisting resin particles is preferably set to range from 5 to 50 weight % and desirably range from 10 to 40 weight % with respect to the solid content of a heat resisting resin matrix.
The heat resisting resin particles are preferably constructed by amino resin (melamine resin, urea resin, guanamine resin), epoxy resin, etc. A acrylic-system monomer can be used.
The adhesive may be constructed by two layers having different compositions.
Various kinds of resins can be used as a solder resist layer added to a surface of the multilayer build-up wiring board. For example, it is possible to use bisphenol A-type epoxy resin, acrylate of bisphenol A-type epoxy resin, novolak type epoxy resin, resin formed by hardening acrylate of novolak type epoxy resin by an amine-system hardening agent, an imidazole hardening agent, etc.
There is a case in which such a solder resist layer is separated since the solder resist layer is constructed by resin having a stiff skeleton. Therefore, the separation of the solder resist layer can be also prevented by arranging a reinforcing layer.
The above acrylate of the novolak type epoxy resin can be constructed by using epoxy resin in which glycidyl ether of phenol novolak and cresol novolak reacts with acrylic acid, methacrylic acid, etc.
The above imidazole hardening agent is desirably formed in a liquid state at 25xc2x0 C. since the imidazole hardening agent can be uniformly mixed in the liquid state.
Such a liquid state imidazole hardening agent can be constructed by using 1-benzyl-2-methylimidazole (product name: 1B2MZ), 1-cyanoethyl-2-ethyl-4-methylimidazole (product name: 2E4MZ-CN) and 4-methyl-2-ethylimidazole (product name: 2E4MZ).
An adding amount of this imidazole hardening agent is desirably set to range from 1 to 10 weight % with respect to a total solid content of the above solder resist composition substance. This is because the imidazole hardening agent is easily. uniformed and mixed if the adding amount lies within this range.
A composition substance prior to the hardening of the above solder resist is desirably constructed by using a solvent of a glycol ether system as a solvent.
In the solder resist layer using such a composition substance, no free acid is caused and no copper pad surface is oxidized. Further, a harmful property with respect to a human body is low.
Such a solvent of the glycol ether system is constructed by using the following structural formula, particularly desirably using at least one kind selected from diethylene glycol dimethyl ether (DMDG) and triethylene glycol dimethyl ether (DMTG). This is because these solvents can perfectly dissolve benzophenone and Michler""s ketone as reaction starting agents at a heating temperature from about 30 to 50xc2x0 C.
CH3Oxe2x80x94(CH2CH2O)nxe2x80x94CH3.
(n=1 to 5)
This solvent of the glycol ether system preferably has 10 to 70 wt % with respect to a total weight amount of the solder resist composition substance.
As explained above, various kinds of antifoaming and leveling agents, thermosetting resin for improving a heat resisting property and an antibasic property and giving a flexible property, a photosensitive monomer for improving resolution, etc. can be further added to the solder resist composition substance.
For example, the leveling agent is preferably constructed by monomer of acrylic ester. A starting agent is preferably constructed by Irugacure 1907 manufactured by CHIBAGAIGI. A photosensitizer is preferably constructed by DETX-S manufactured by NIHON KAYAKU.
Further, a coloring matter and a pigment may be added to the solder resist composition substance since a wiring pattern can be hidden. This coloring matter is desirably constructed by using phthalocyaline green.
Bisphenol type epoxy resin can be used as the above thermosetting resin as an adding component. In this bisphenol type epoxy resin, there are bisphenol A-type epoxy resin and bisphenol F-type epoxy resin. The former is preferable when an antibasic property is seriously considered. The latter is preferable when low viscosity is required (when a coating property is seriously considered).
A polyhydric acrylic-system monomer can be used as the above photosensitive monomer as an adding component since the polyhydric acrylic-system monomer can improve resolution. For example, DPE-6A manufactured by NIHON KAYAKU and R-604 manufactured by KYOEISYA KAGAKU can be used as the polyhydric acrylic-system monomer.
These solder resist composition substances preferably have 0.5 to 10 Paxc2x7s in viscosity at 25xc2x0 C. and more desirably have 1 to 10 Paxc2x7s in viscosity since these solder resist composition substances are easily coated by a roll coater in these cases.
In claim 34, a method of manufacturing a multilayered printed circuit board such that a through hole is formed in a double-side copper-plated laminated board by performing a laser machining and the through hole is made to be conductive to form a through hole so that a core substrate is manufactured, and
an interlayer insulating resin layer and a conductive circuit are formed on the core substrate, said method of manufacturing a multilayered printed circuit board comprising the step of:
making the thickness of copper foil of the double-side copper-plated laminated board to be smaller than 12 xcexcm.
In claim 37, a substrate for forming a through hole such that a through hole is formed in a double-side copper-plated laminated board and the through hole is made to be conductive so that a through hole is formed, said substrate comprising:
taper provided for the through hole.
In claim 40, a multilayered printed circuit board incorporating a substrate in the form of a double-side copper-plated laminated board in which a through hole is formed such that the through hole is made to be conductive so that a through hole is formed and an interlayer insulating resin layer and a conductive circuit are formed on at least either side of the substrate, said multilayered printed circuit board comprising:
taper provided for the through hole.
As a result of energetic studies performed by the inventors of the present invention, the following fact was detected: the reason why an opening cannot be formed in copper foil having a thickness of 12 xcexcm by the carbon-dioxide gas laser beam is not reflection at the surface. The foregoing fact is caused from the large thickness of the copper foil with which thermal conduction easily occurs. Thus, the energy of the laser beam is converted into heat which is undesirably conducted.
The thickness of the copper foil is smaller than 12 xcexcm, preferably about 1 xcexcm to about 10 xcexcm. Thus, conversion of the energy of the laser beam into heat which is conducted as described above can be prevented. Thus, formation of an opening using the laser beam can be realized.
The copper-plated laminated board according to the present invention may be a copper-plated laminated board obtained by bonding copper foil to prepreg, such as glass-cloth epoxy resin, glass-cloth bis maleimide-triazine resin or glass-cloth fluororesin.
It is preferable that the thickness of the copper foil is 1 xcexcm to 10 xcexcm. The reason for this lies in that an opening can easily be formed by the laser beam if the thickness is 10 xcexcm or smaller. If the thickness is smaller than 1 xcexcm, blister or the like occurs.
The thickness of the copper foil is adjusted by etching. Specifically, chemical etching is employed which uses sulfuric acid and hydrogen peroxide solution, ammonium persulfate solution, cupric chloride solution or ferric chloride solution; or physical etching, such as ion-beam etching is employed.
It is preferable that the thickness of the copper-plated laminated board is 0.5 mm to 1.0 mm. If the thickness is too large, the opening cannot be formed. If the thickness is too small, warp or the like occurs.
It is preferable that the carbon-dioxide gas laser beam for use in the present invention is a short-pulse laser of 20 mJ to 40 mJ and 10xe2x88x924 second to 10xe2x88x928 second.
The number of shots of the laser beams is 5 shots to 100 shots.
It is preferable that the diameter of the through hole which must be formed is 50 xcexcm to 150 xcexcm. If the thickness is smaller than 50 xcexcm, the surface of the wall cannot be made to be conductive by plating or the like. If the thickness is larger than 150 xcexcm, a drill work enables an advantage to be realized.
If the diameter of the through hole is larger than 100 xcexcm, the through hole encounters taper. Taper occurs on the side on which the laser beam is made incident such that the diameter of the through hole is enlarged.
When the laser beam is applied from the right side or the reverse side, a through hole having a cross section formed into a concave shape is undesirably formed.
The foregoing through hole is made to be conductive by electric plating, electroless plating, sputtering, evaporation or enclosure of conductive paste.
When the conductive paste is enclosed, it is preferable that taper is provided for the through hole to easily enclose the paste.
Also in a case where the through hole is formed by metalizing the surface of the inner wall by electric plating, electroless plating, sputtering or evaporation, the through hole can be filled with a filler.
The inner wall of the metalized through hole may be coarsened.
When the inner wall of the through hole is metalized, it is preferable that each of the thickness of the copper foil and that of the metalized layer (for example, the electroless plated layer) is 10 xcexcm to 30 xcexcm.
The filler may be any one of a variety of materials including a filler constituted by inorganic particles made of bis phenol F epoxy resin, silica or alumina, metal particles and resin.
The conductive circuit is provided for the substrate having the through hole structured as described above. The conductive circuit is formed by an etching process.
It is preferable that the surface of the conductive circuit is subjected to a coarsening process in order to improve the adhesiveness.
Then, the interlayer insulating resin layer made of insulating resin is formed.
The insulating resin may be thermosetting resin, thermoplastic resin or their composite resin. In the present invention, the interlayer insulating resin layer may be adhesive agent for electroless plating. The opening can be formed in the foregoing interlayer insulating resin layer by a laser beam, exposure or a development process.
In claim 45, a built-up multilayered printed circuit board according to comprising: a substrate having a through hole and a conductive circuit and structured such that interlayer insulating resin layers and conductive circuits are alternately formed and the conductive circuits in the different layers are electrically connected to one another through via holes formed in the interlayer insulating resin layers, wherein
the substrate is a glass epoxy resin substrate made of epoxy resin having Tg point of 190xc2x0 C. or higher.
As a result of energetic studies performed by the inventors of the present invention, the following fact was detected: the reason why the insulation resistance between the through holes is reduced during the HAST test and the steam test is that metal, such as copper, which forms the through hole is ionized and ions are moved (migration) between the through holes, causing the insulation resistance to be reduced.
Another fact was found that the resistance of the conductive circuit which connects the through holes to each other after the heat cycle test lies in that thermal expansion and contraction result in the conductive circuit resist the plated through hole being broken.
A fact was detected that the migration and thermal expansion and contraction can be prevented by raising the crosslinking density of the epoxy resin to raise the Tg point.
If the Tg point of the epoxy resin is not lower than 190xc2x0 C., the foregoing problems can be prevented. As a result, the ionization of the metal which forms the through hole and ions are moved (migration) as described above to reduce the insulation resistance between the plated through holes during the HAST test and the steam test can be prevented. Moreover, the thermal expansion and contraction occurring in the heat cycle test resulting in the conductive circuit or the through hole being broken and thus the resistance is changed, can be prevented.
Note that the epoxy resin is low-cost resin as compared with BT resin.
As the glass epoxy resin substrate having a Tg point of 190xc2x0 C. or higher (a DMA method (temperature rise rate: 2xc2x0 C./minute)), a known substrate developed for a mass-lamination type multilayered printed circuit board may be used.
For example, any one of the foregoing materials may be employed: HL830 (Tg point: 217xc2x0 C.) or HL830FC (Tg point: 212xc2x0 C.) manufactured by Mitsubishi Gas Chemical, MCL-E-679LD (Tg point: 205xc2x0 C. to 215xc2x0 C.) or MCL-E-679F (Tg point: 205xc2x0 C. to 217xc2x0 C.) manufactured by Hitachi Chemical or R-5715 (Tg point: 190xc2x0 C.) manufactured by Matsushita Electric Works.
An opening is, by a laser beam or drilling, formed in the foregoing glass epoxy resin substrate or the copper-plated laminated board, followed by metalizing the surface of the inner wall by electric plating, electroless plating, sputtering or evaporation. Thus, the through hole is formed. A filler may be enclosed in the foregoing through hole.
The metalized inner wall of the through hole may be coarsened.
The filler may be made of any one of a variety of materials including inorganic particles made of bis phenol F epoxy resin, silica or alumina; or metal particles; and resin.
The conductive circuit is provided for the thus-formed substrate having the through hole formed therein. The conductive circuit is formed by an etching process.
It is preferable that the surface of the conductive circuit is subjected to the coarsening process.
Then, the interlayer insulating resin layer is formed. The insulating resin may be thermosetting resin, thermoplastic resin or their composite resin.
To solve the problem, in claim 46, a method of manufacturing a printed circuit board incorporating through holes and conductor patterns formed by a subtractive method, said method of manufacturing a printed circuit board according to the present invention comprising:
an opening forming step for forming an opening for forming a through hole at a predetermined position of a metal-applied board formed by applying conductive metal foil having a thickness of 0.5 xcexcm to 7.0 xcexcm to each of two sides of an insulating substrate;
a desmear step for dissolving and removing smear existing in the opening for forming the through hole;
a first plating step for forming a thin plated layer on a ground layer caused from the conductive metal foil and the surface of the inner wall of the opening for forming the through hole;
a second plating step for forming a mask on the thin plated layer and forming a thick plated layer on a portion exposed through an opening of the mask; and
performing etching after the mask has been separated so that the thin plated layer and the ground layer below the mask are removed so as to divide the conductor patter.
An aspect of claim 46 enables smear taken place during an opening forming process to be dissolved and removed by performing a desmear process. Also the conductive metal foil is dissolved and removed at this time. Thus, the conductive metal foil is thinned. A first plating process is performed so that a thin plated layer is formed. Then, a second plating process is performed so that a thick plated layer is formed. As a result, only portions which will be formed into the conductive pattern are selectively thickened. Then, etching is performed so that the thin plated layer below the mask and the ground layer are removed. Thus, the conductive pattern is divided. In the present invention, both of the thin plated layer and the ground layer are thin layers. Therefore, the thickness which must be removed by etching performed in the conductive pattern dividing step is very small. Therefore, formation of a divergent shape of the conductive pattern formed by dividing does not easily occur. Thus, a fine pattern having a satisfactory shape can accurately be formed.
The conductive metal foil can be made with copper s aluminum, gold, silver, platinum or nickel. Specifically, the copper or the metal mainly comprising the copper is desirable.
The present invention in claim 48 according to claim 48, the first plating step uses an electroless plating bath, and the second plating step uses an electrolytic plating bath.
An aspect of claim 48 has a structure that the electroless plating bath is employed only when the plated layer is formed on the inner wall of the opening for forming the through hole. Then, the low-cost electrolytic plating bath which exhibits high speed plating deposition speed is employed. As a result, the cost reduction can be realized and the productivity can be improved.
The present invention in claim 49 according to claim 47, the first plating step uses an electroless copper plating bath to form a copper plated layer having a thickness of 0.2 xcexcm to 2.5 xcexcm, and the second plating step uses an electrolytic copper plating bath to form a copper plated layer having a thickness of 8.0 xcexcm or greater.
An aspect of claim 49 has a structure that the electroless plating bath is employed only when the plated layer is formed on the inner wall of the opening for forming the through hole. Then, the low-cost electrolytic plating bath which exhibits high speed plating deposition speed is employed. As a result, the cost reduction can be realized and the productivity can be improved. Since a very-thin copper plated layer is formed in the first plating step, the thickness which must be removed by etching in the conductive pattern dividing step is very small. Therefore, a fine pattern having a satisfactory shape can furthermore accurately be formed.
The present invention in claim 50 according to any of claims 47 to 49, the step for dividing the conductor pattern by performing etching is performed in a state in which no etching resist is provided for the thick plated layer formed in the second plating step.
An aspect of claim 50 has a structure that the step for forming and separating the etching resist in the conductive pattern dividing step can be omitted. Thus, the number of manufacturing steps can be reduced and the productivity can be improved. Moreover, the thickness of the thick plated layer which is removed when the etching process is performed is very small. Thus, no adverse influence is exerted on the accuracy of the formed pattern.
According to another aspect of the present invention in claim 51, a printed circuit board incorporating a conductive pattern is provided which is formed by, for example, subtractive method, wherein the conductive pattern includes a metal ground layer provided for an insulating substrate and having a thickness of 0.2 xcexcm to 3.0 xcexcm and a plated layer formed on the metal ground layer.
According to another aspect of the present invention in claim 52, there is a printed circuit board provided, wherein the conductive pattern includes a metal ground layer provided for an insulating substrate and having a thickness of 0.2 xcexcm to 2.5 xcexcm, a plated layer formed on the metal ground layer and having a thickness of 0.2 xcexcm to 2.5 xcexcm and a plated layer formed on the plated layer and having a thickness of 8.0 xcexcm or greater.